fix enum values

when the first member is assigned 0, vala assigns 0 to the next member
regardless

core/src/widget/button.vala

@@ -33,7 +33,7 @@ public class Button : Gtk.Button {
 }
 
 public enum MouseButton {
-    PRIMARY = 0,
+    PRIMARY,
     MIDDLE,
     SECONDARY,
     BACK,

core/src/widget/icon.vala

@@ -81,7 +81,7 @@ public class Icon : Gtk.Image {
             type = IconType.GICON;
             display_icon.begin();
         });
-        
+
         size_allocate.connect(() => {
             size = get_style_context()
                 .get_property("font-size", Gtk.StateFlags.NORMAL).get_double();